1. Field of the Invention
The invention relates to equipment for locating and/or characterizing a reflection point in a transmission line by recording the impulse response of the path of an echo produced at said reflection point in response to a transmission signal, said equipment comprising a transmission path and a reception path coupled to the transmission line by a coupling circuit, the transmission signal being derived from a reference signal constituted by binary sequences of the same duration NT equal at least to twice the propagation time in the transmission line, N being an integer and T being the duration of a bit.
The equipment envisaged may be used in particular for the location and characterization of a result of a fault in a transmission line. It is known that if at some point in a transmission line a fault occurs that gives rise to an irregularity in the electric parameters, the value of the characteristic impedance at that point will be modified and any incident wave will give rise to a reflected wave called an "echo". Measurement, at the input of the transmission line, of the time separating the transmission of an incident wave and the return of the reflected wave makes it possible, the propagation speed being known, to determine the distance between the point of measurement and the location of the fault. In addition, the phase and amplitude characteristics of the reflected wave enable the nature of the fault to be determined (short-circuit, open circuit or grounding) as well as its intensity.
2. Description of the Prior Art
Among the equipments utilizing echo measurements for locating and characterizing faults in transmission lines, relatively rudimentary workshop equipments are known in which the locating and characterization of the fault are preformed by an operator observing a display screen on which there appears the echo signal received in response to a transmitted pulse.
This type of equipment often requires manual adjustment of the balance impedance of the coupling circuit, while the measurements may be very disturbed by the line noise. Furthermore, with this type of equipment it is not possible, for example, to provide for automatic maintenance of all the subscriber lines connected to a telephone exchange. For that it is necessary, as in the equipment envisaged, for all the echo measurements to be recorded automatically in a memory in digital form, for subsequent processing by a computer.
The U.S. Pat. No. 4,041,381 also describes an equipment enabling the location and characterization of a fault in a transmission line. In this equipment a train of identical pulse sequences is transmitted along a transmission line, the autocorrelation function of the sequences being an impulse function. Correlation calculations are made between the received signal and the transmission sequences successively delayed by steps of time delay until there is found in the calculated signal a peak indicating the correlation between the transmitted signal and the received signal. This process can provide a digital recording of the impulse response of the echo path, but it has the drawback of requiring a substantial volume of calculations and of memory capacity, as well as being sensitive to noise on the transmission line, which limits the maximum distance at which a fault can be detected.